Hydraulic control circuit



July 15, 1969 D. S. PRESTON ETAL HYDRAULIC CONTROL CIRCUIT Filed Feb.25, 196'? lllllll I v ATTORNEYS 3,455,209 HYDRAULIC CONTROL CIRCUITDavid S. Preston, Euclid, and Richard H. Stroh, Richmond Heights, Ohio,assignors to Eaton Yale & Towne Inc., a corporation of Ohio Filed Feb.23, 1967, Ser. No. 617,990 Int. Cl. F15b 15/17, 13/08, 21/00 US. Cl.91-417 5 Claims ABSTRACT OF THE DISCLOSURE This invention relates to theart of machine control mechanisms, and more particularly to a hydrauliccontrol circuit.

The present invention is particularly applicable to controlling theoperation of materials handling equipment, such as cranes, fork-liftsand the like, and it will be described with particular referencethereto; however, it will be appreciated that the invention has broaderapplications and may be used to control the operation of other types ofmachines.

In a class of materials handling equipment known in the trade as stackercranes, heavy loads, and in some designs even portions of the cranes,such as telescoping mast sections, are raised under force of hydraulicfluid, held suspended by hydraulic pressure while the loads aretranslocated, and then lowered by the weight of the load or the combinedweight of the load of suspended crane portions.

Hydraulic control circuits for such equipment usually include a pistonand a cylinder coactive for relative movement therebetween; a port inthe cylinder; high pressure conduit means communicating with the port; asource of high pressure fluid; a fluid reservoir; control valve meansconnected to the high pressure conduit means, and operative selectivelyto communicate the source of high pressure fluid and the fluid reservoirwith the high pressure conduit means.

Almost invariably, the hydraulic control systems for a stacker craneinclude flexible hose pOrtiOns to permit full manipulation of the crane.These hoses deteriorate in time as a result of exposure to highpressure, heat and fatigue through flexure. Since rupture of the hosesis an everpresent danger, safety devices should be provided to protectpersonnel and equipment against injury and damage due to loss ofhydraulic pressure through a ruptured hydraulic hose.

The present invention contemplates a fail safe mechanism which will holdthe load and suspended crane portions in a fixed position in the eventof a failure of hydraulic pressure.

In accordance With the present invention, a fail safe mechanismoperative to stop relative mOvement between the piston and cylinder inthe event of fluid pressure failure is provided, comprised of a pilotoperated check valve ositioned in line with the high pressure conduitmeans near the cylinder port, the check valve being operative to closeupon loss of pilot pressure; and a pilot pressure line communicating thecheck valve with the high pressure conduit means at a point near thecontrol nite States Patent 0 3,455,209 Patented July 15, 1969 valvemeans, whereby failure of pressure in the high pressure conduit meanscauses a loss of pressure in the pilot pressure line, closing the checkvalve.

Hydraulic equipment for raising and lowering heavy mass usually employsa single acting piston, the load being lowered by simple bleeding of thefluid from the pressure end of the piston. Such a system presentsproblems of leakage past the piston and other difliculties.

The invention also contemplates a hydraulic control circuit of the typedescribed having improved efliciency by employing a double actinghydraulic cylinder and maintaining the blind end of the cylinderback-filled with hydraulic fluid under nominal pressure. Thus,substantially the entire volume of the cylinder is kept filled withhydraulic fluid at all times. This arrangement reduces the size of thefluid reservoir needed for a given system, and serves as a heatexchanger for hydraulic fluid, reducing or eliminating the requirementfor external cooling means.

In accordance with this aspect of the invention, there is providedadditionally a second port communicating with the interior of thecylinder member near the opposite end thereof for admitting low pressurefluid when the mass is lowered and withdrawing low pressure fluid whenthe mass is raised; a low pressure relief valve; a low pressure conduitcommunicating the relief valve with the second cylinder port formaintaining fluid at a predetermined low pressure head; and amnlti-position control valve operative selectively to communicate thehigh pressure conduit with the source of high pressure fluid and withthe fluid reservoir, and selectively to communicate the low pressureconduit with a source of low pressure fluid and with the fluidreservoir, the control valve having one position effective to raise themass under force of hydraulic fluid, wherein the high pressure source isin communication with the high pressure conduit and th first cylinderport, and the second port and low pressure conduit are in communicationwith the fluid reservoir, the control valve having another positioneffective to permit the mass to be lowered, wherein the first cylinderport and the high pressure conduit are in communication with the fluidreservoir and the source of high pressure fluid is in combination withthe low pressure conduit, the relief valve and the second cylinder port.

It is, therefore, an object of the invention to provide an improvedhydraulic control circuit.

Another object of the invention is to provide a hydraulic controlcircuit with a fail safe mechanism of improved construction.

A further object of the invention is to provide a hydraulic controlcircuit of improved efliciency.

These and other objects and advantages will become apparent from thedetailed description of a preferred embodiment of the invention whenread in connection with the accompanying drawing, in which the solefigure is a schematic circuit diagram illustrating a preferredembodiment of the present invention.

Referring now to the drawing, wherein the showings are for purposes ofillustrating a preferred embodiment of the invention only and not forpurpose of limiting the same, the figure shows a hydraulic controlcircuit comprised of piston 10 and cylinder 12 coactive for relativemovement therebetween. As shown in the preferred embodiment, piston 10is fixed, while cylinder 12 is mounted for relative movement withrespect to the piston. It will be understood however, that thearrangement can be reversed, making cylinder 12 fixed and piston 10movable with respect to the cylinder.

In the arrangement illustrated, a mass (not shown) is suspended fromcylinder 12 for movement therewith. As applied to a stacker crane, themass may take the form of a load to be moved from one place to another,or the combination of such a load with suspended portions of the crane.The circuit illustrated is operative to raise the mass under force ofhydraulic fluid, and lower the mass under its own weight.

The hydraulic control circuit further comprises a port 14 near one endof cylinder 12 for admitting high pressure fluid when the mass israised. High pressure conduit means such as line 16 is provided tosupply high pressure fluid to cylinder 12 through port 14.

Cylinder 12 is further provided with a second port 18 positioned nearthe opposite end thereof for admitting low pressure fluid when the massis lowered and withdrawing low pressure fluid when the mass is raised.Low pressure conduit means such as line 20 communicates low pressurefluid with port 18 and cylinder 12. Low pressure relief valve 22communicates with line 20 to maintain low pressure hydraulic fluid at apredetermined head. Relief valve 22 communicates with fluid reservoir34.

The circuit is further provided with a source of high pressure fluid,such as pump 26 driven by motor M. Hydraulic fluid from pump 26 travelsthrough line 28, check valve 30 and into valve means for controllingrelative movement between piston and cylinder 12, which may take avariety of forms but in the preferred embodiment illustrated, takes theform of a multi-position control valve 32.

High pressure line 16 is provided with pilot operated check valve 36positioned near port 14, and the valve is provided with pilot pressureline 38 which runs parallel to high pressure line 16 connecting with thelatter at a point near multi-position control valve 32. Consequently,the same pressure which is present in line 16 is also present in pilotpressure line 38, to activate pilot operated check valve 36. Pilotpressure fluid is also provided by pilot pressure pump 40, communicatingwith line 42, check valve 44 which in turn communicates with highpressure line 16.

High pressure line 16 is also provided with adjustable needle valve 46and check valve 48 in parallel. Check valve 48 is designed to permithydraulic fluid to pass from multi-position control valve 32 to port 14,but not in the opposite direction. Fluid can flow through needle valve46 in both directions.

The positions of multi-position control valve 32 are marked a, b and cin the drawing. Position a is effective to raise the mass under force ofhydraulic pressure, by providing communication from pump 26 through line28, check valve 30, high pressure line 16, pilot operated check valve36, port 14, and cylinder 12. The force of hydraulic fluid forcescylinder 12 to raise itself against stationary piston 10. Position a ofmulti-position control valve 32 also communicates port 18 and line 20with lines 50 and reservoir 34, and line 24 through pressure relief 22to reservoir 34. Thus, as cylinder 12 is raised low pressure fluid isforced out of the bottom of the cylinder through port 18, line 20 andthence through lines 24, 50 to reservoir 34. The low pressure head ismaintained on this part of the system by relief valve 22.

In order to stop the relative movement between cylinder 12 and piston 10at any point, multi-position control valve 32 is moved to position B. Inthis position, lines 16, 20 are blocked with respect to lines 28, 50. Inthis manner, cylinder 12 is held in a fixed position, subject to slightmovement due to leakage of high pressure fluid in the top half of thecylinder, past the head of piston 10 into the lower pressure chamber inthe bottom half of the cylinder. A pressure built up in the bottom halfof the cylinder is prevented by pressure relief valve 22. In position b,the supply of fluid from pump 26 passes through valve 32 to line 50 andthence, to reservoir 34.

To lower the mass suspended from cylinder 12, multiposition controlvalve 32 is moved to position c. Under the weight of the mass suspendedfrom cylinder 12, high pressure fluid travels out of the cylinderthrough port 14, pilot operated check valve 36, high pressure line 16,needle valve 46, through line 50 and into reservoir 34. Due to thepositioning of check valve 48, all of the high pressure fluid travelsthrough needle valve 46, which limits the rate of descent of the masssuspended from cylinder 12.

The lowering of the mass permits the entry of additional low pressurefluid through line 20, port 18 and into the interior of the lowerportion of cylinder 12. This fluid comes from the high pressure line 28,through check valve 30, where the high pressure fluid is vented byrelief valve 22, providing a source of low pressure fluid into line 20,port 18 and the interior of cylinder 12. Excess hydraulic fluidtraveling through line 24, relief valve 22 enters reservoir 34.

As previously described, pilot operated check valve 36 will remain openonly so long as pilot pressure of a predetermined minimum head ispresent on line 38. During raising of the mass, when high pressure fluidcommunicates with line 16, and port 14, the same high pressure fluid ispresent in pilot pressure line 38. However, when the mass is lowered,the pressure in line 16 may drop to a level below the predeterminedminimum required to maintain pilot operated check valve 36 open. In thisevent, supplemental pilot pressure generated by pump 40 travels throughline 42, check valve 44 and into high pressure line 16. Due to theinterconnection of high pressure line 16 and pilot pressure line 38,this auxiliary pressure will maintain a minimum predetermined pilotpressure in line 38.

In the event that high pressure line 16 ruptures, due to a failure of aflexible portion thereof, pilot pressure in line 38 will immediately belost, due to the parallel arrangement of line 38 with line 16. With aloss of pilot pressure, pilot operated check valve 36 will close,sealing high pressure fluid within the upper portion of cylinder 12.This in turn will cause a stoppage of relative movement be tweencylinder 12 and piston 10. This fail safe mechanism will prevent anuncontrolled descent of the mass suspended from cylinder 12, preventinginjury to personnel and damage to equipment.

As will be noted, substantially the entire volume of cylinder 12 ismaintained filled with hydraulic fluid, by 'keeping the dead end of thecylinder back filled with low pressure hydraulic fluid through line 20and port 18. In this way, the size of the reservoir required for thesystem is substantially reduced. In addition, the travel of hydraulicfluid through the low pressure lines and into the lower half of thecylinder, permits some of the heat in the fluid to transfer to the linesand the cylinder, thus, reducing or eliminating the requirement forexternal cooling means.

Having thus described our invention, we claim:

1. A hydraulic control circuit comprised of a piston and a cylindercoactive for relative movement therebetween; a port in said cylinder; asource of high pressure fluid; a fluid reservoir; control valve meansremote from said piston and cylinder; a first high pressure conduitmeans communicating said source and said reservoir with said controlvalve means; a second high pressure conduit communicating with said portand said control valve means; said control valve means being operativeselectively to communicate said source of high pressure fluid and saidfluid reservoir with said second high pressure conduit means; and a failsafe mechanism operative to stop relative movement between said pistonand said cylinder in the event of fluid pressure failure; comprised of apilot operated check valve positioned in line with said high pressureconduit means near said cylinder port, said check valve being operativeto close upon loss of pilot pressure; and an independent pilot pressureline in parallel with and communicating said check valve with saidsecond high pressure conduit means at a point near said control valvemeans, whereby failure of pressure in said second high pressure conduitmeans causes a loss of pressure in said pilot pressure line, closingsaid check valve.

2. The hydraulic control circuit as defined in claim 1, furthercomprising a source of low pressure fluid, of a head great enough toactuate said pilot operated check valve; low pressure conduit meanscommunicating said source of low pressure fluid with said second highpressure conduit means, and via the last mentioned means, with saidpilot pressure line; and a check valve in said low pressure line andoperative to permit fluid flow only in a direction from said lowpressure source to said second high pressure conduit, whereby duringnormal operation of said control circuit a head of pressure great enoughto actuate said pilot operated check valve is always present in saidpilot pressure line.

3. A hydraulic control circuit operative to raise a mass under force ofhydraulic fluid and lower a mass under its own weight comprising: acylinder member; a piston member mounted therein, wherein one of saidmembers is fixed, and the other of said members is movable along areciprocative path, said movable member being adapted to support a masswhereby movement in one direction along said reciprocative path raisessaid mass, and movement in the opposite direction along saidreciprocative path lowers said mass; a first port communicating with theinterior of said cylinder member near one end thereof, for admittinghigh pressure fluid when said mass is raised and withdrawing highpressure when said mass is lowered; a high pressure conduit connected tosaid first port; a second port communicating with the interior of saidcylinder member near the opposite end thereof for admitting low pressurefluid when said mass is lowered and withdrawing low pressure fluid whensaid mass is raised; a low pressure relief valve; a low pressure conduitcommunicating said relief valve with said second port for maintainingsaid low pressure fluid at a predetermined head; a source of highpressure fluid; a fluid reservoir; a multi-position control valveoperative selectively to communicate said high pressure conduit withsaid source of high pressure fluid and with said fluid reservoir, andselectively to communicate said low pressure conduit with said source ofhigh pressure fluid and with said fluid reservoir, said control valvehaving one position effective to raise said mass under force ofhydraulic fluid, wherein said high pressure source is in communicationwith said high pressure conduit and said first cylinder port, and saidsecond cylinder port and low pressure conduit are in communication withsaid fluid reservoir, said control valve having another positioneffective to permit said mass to be lowered under its own weight,wherein said first cylinder port and said high pressure conduit are incommunication with said fluid reservoir and said source of high pressurefluid is in communication with said low pressure conduit, said reliefvalve and said second cylinder port; and a fail safe mechanism operativeto stop relative movement between said piston member and said cylindermember in the event of fluid pressure failure, comprising a pilotoperated check valve interposed between said first port and said threeposition control valve in said high pressure conduit means, said checkvalve being operative to close upon loss of pilot pressure; and anindependent pilot pressure line in parallel with and communicating saidcheck valve with said high pressure conduit means, whereby failure ofpressure in the latter causes a loss of pilot pressure closing saidcheck valve.

4. The hydraulic control circuit as defined in claim 3, wherein saidhigh pressure conduit is provided with an adjustable needle valve and acheck valve in parallel, said check valve permitting fluid flow only ina direction from said control valve to said first cylinder port, wherebyfluid withdrawn from said cylinder through said first port upon loweringsaid mass passes only through said needle valve at a rate controlledthereby, while fluid entering said cylinder through said first cylinderport, upon raising said mass, passes through both said needle valve andsaid check valve in parallel therewith.

5. A hydraulic control circuit including a cylinder member; a pistonmember mounted therein, wherein one of said members is fixed, and theother of said members is movable along a reciprocative path; workproducing means suspended from and movable with said movable member formovement between a position of higher potential energy and a position oflower potential energy, a first port communicating with the interior ofsaid cylinder member near one end thereof for admitting and withdrawinghigh pressure fluid; a second port communicating with the interior ofsaid cylinder member for admitting and withdrawing low pressure fluid, arelief valve communicating with said second port for maintaining saidlow pressure fluid at a predetermined head; a source of high pressurefluid; a fluid reservoir; valve means for controlling relative movementbetween said piston member and said cylinder member, comprising a threeposition control valve, having (1) a first position operative tocommunicate said source of high pressure fluid via high pressure conduitmeans with said first port, and communicate said fluid reservoir via lowpressure conduit means with said second port, causing said movablemember to move in one direction along its reciprocative path and saidwork producing means suspended therefrom to move from a position oflower potentlal energy to a position of higher potential energy; (2) asecond position operative to block communication between said source ofhigh pressure fluid and said first port, and to block directcommunication between said fluid reservoir and said second port, wherebysaid movable member and said work producing means suspended therefromare held in fixed positions; and (3) a third position operative tocommunicate said fluid reservoir with said first port and to communicatesaid source of high pressure fluid with said relief valve and saidsecond port, causing said movable member to move in an oppositedirection along its reciprocative path, under the urging of said workproducing means suspended therefrom, moving from a position of higherpotential energy to a position of lower potential energy; and a failsafe mechanism operative to stop relative movement between said pistonmember and said cylinder member in the event of fluid pressure failure,comprising a pilot operated check valve interposed between said firstport and said three position control valve in said high pressure conduitmeans, said check valve being operative to close upon loss of pilotpressure; and an independent pilot pressure line in parallel with andcommunicating said check valve with said high pressure conduit means,whereby failure of pressure in the latter causes a loss of pilotpressure closing said check valve.

References Cited UNITED STATES PATENTS 2,860,607 11/1958 Orlolf.3,047,017 7/ 1962 Brinkel. 3,065,739 11/1962 Boroson 91-445 3,202,060 8/1965 Grotness 91-443 FOREIGN PATENTS 632,201 12/1961 Canada.

CARROLL B. DORITY, 111., Primary Examiner US. Cl. X.R.

